Question

Q. The sum of the first 16 terms of an AP whose first term and third term are 5 and 15 respectively is

• A. 680
• B. 600
• C. 640
• D. 620

Answer 1

The correct option is A 680

a = 5 $\to$ (1
a + 2d = 15 $\to$ (2
(2 - (1
= 2d = 10
d = 5
$S_{16}=8\times \left(\right(2\times 5)+(15\times 5\left)\right)$
= 680